Existing high pressure aircraft engine fuel pumps are typically positive displacement pumps such as gear pumps or vane pumps. In such pumps, shaft seals can be located in low pressure cavities whereby the seals are not subjected to high pressure.
High speed centrifugal fuel pumps capable of developing high fuel pressures (e.g., 700 psi) are now being seriously considered for aircraft engine applications. In general, high speed centrifugal pumps are mounted for rotation by means of ball bearings which are lubricated by oil. Oil lubrication of the bearings mandates the inclusion of a dual fuel to oil seal with an overboard drain therebetween. Since the fuel pressure developed by a high speed centrifugal pump is relatively high, a failure in a fuel seal can result in flooding of the overboard drain cavity and a consequential fuel leak into the oil cavity.